The invention relates to a method for cold-rolling sheets and strips.
The surface evenness of cold-rolled sheets and strips can be distorted in different manners. Thus there may be, for example, strip curvature, long strip center short strip edges, long strip sides, edge waves, localized wave paths and short strip fibers and also the combined appearance of different faults in surface evenness, such as are shown in overview in FIG. 1 of the publication by E. Neuschutz in the book "Walzen von Flachprodukten" (Rolling of flat products), Informationsgesellschaft-Verlag, 1987, pages 7 to 26. The causes of such faults in surface evenness are unsuitable adjustment of the rollers, an unsuitable ground surface of the rollers, wear of the rollers, temperature differences over the barrel width of the rollers, differences in hardness in the strip and the embedding behavior of the strip at the strip edges.
By specific action on appropriate adjusting members of the rolling mill, the faults in surface evenness can be counteracted, it being possible to establish regulating circuits (control loops) with the surface evenness as a standard variable. For example, DE-OS 32 40 602.9 provides that, for regulating the tensile stress distribution during cold-rolling of strips on the basis of measurements of the tensile stress distribution, the adjusting members for the roller gap are positioned in such a manner that the differences between the tensile stress at the feed and the delivery sides of the rolling mill are maintained as constant as possible over the roller width and below a maximum value above which folding occurs during rolling. In that case, however, numerous faults in surface evenness still remain unconsidered which could be overcome by action on further adjusting members.
In total, in a modern six-roller mill, there are up to eight possible positions in order to ensure the surface evenness of the layer of the strip. For example, there may be included among the possible positions the pivoting of the rollers, the bending of the rollers by force at the roller barrel, an axial displacement of the rollers, for example, of the so-called intermediate rollers or by working rollers having different contours, the crossing of the rollers and influencing the roller cambering by cooling or heating on the one hand or by internal pressure of hollow rollers on the other hand. These adjusting members have a different time response as a result of which they are able to achieve their preset values in different times. For example, the deflection of the rollers can be carried out virtually without inertia so that there is no speed dependence, whereas an axial displacement of working rollers or of back-up rollers is speed-dependent because it cannot be carried out on stationary rollers. Thus, deviations which are no longer adjustable may occur with corresponding distortions.